The present invention is directed to a process for forming images with toners. More specifically, the present invention is directed to a process wherein toner images are coated with a curable liquid in which the toner is at least partially soluble, followed by curing the image to a solid. One embodiment of the present invention is directed to a process for forming images which comprises generating an electrostatic image on an imaging member, developing the electrostatic image with a toner, optionally transferring the developed toner image from the imaging member to a substrate, applying to the developed toner image a curable liquid in which the toner is at least partially soluble, and curing the image to a solid.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. For example, U.S. Pat. No. 2,297,691 discloses an electrophotographic imaging process that entails placing a uniform electrostatic charge on a photoconductive insulating layer, such as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. When the toner is charged to a polarity opposite to that of the latent electrostatic image on the photoreceptor, the toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. When the toner is charged to the same polarity as that of the charge applied to the photoreceptor, the toner will normally be attracted to those areas which have been discharged; this process is known as discharge area development. This developed image may then be transferred to a substrate such as paper and subsequently be permanently affixed to the substrate.
In ionographic imaging processes, a latent image is formed on a dielectric image receptor or electroreceptor by ion deposition, as described, for example, in U.S. Pat. Nos. 3,564,556, 3,611,419, 4,240,084, 4,569,584, 2,919,171, 4,524,371, 4,619,515, 4,463,363, 4,254,424, 4,538,163, 4,409,604, 4,408,214, 4,365,549, 4,267,556, 4,160,257, and 4,155,093, the disclosures of each of which are totally incorporated herein by reference. Generally, the process entails application of charge in an image pattern with an ionographic writing head to a dielectric receiver that retains the charged image. The image is subsequently developed with a developer capable of developing charge images.
Processes entailing the overcoating of images are known. For example, U.S. Pat. No. 4,477,548 (Harasta et al.), the disclosure of which is totally incorporated herein by reference, discloses curable coating compositions useful for protective treatments of elements bearing electrographically formed toner images which comprise (a) either (i) a mixture of a siloxy-containing polycarbinol and an acrylated urethane, or (ii) a siloxy-containing acrylated urethane, (b) a multifunctional acrylate, and, optionally, (c) a free radical photoinitiator. Toner image bearing elements, such as electrographic elements and specifically photoconductive recording films, can be provided with a protective overcoat layer which is bonded to the element and which serves to protect the toner image from abrasion and scratches. Such an overcoat layer is provided by coating the element with a curable composition and curing the resulting coating. The protective overcoat layer is applied to the toner image-bearing side of the element.
U.S. Pat. No. 4,426,431 (Harasta et al.), the disclosure of which is totally incorporated herein by reference, discloses radiation-curable compositions useful for restorative and/or protective treatment of photographic elements which comprise a polymerizable epoxy compound, a cationic initiator for initiating polymerization of the epoxy compound, a polymerizable acrylic compound, a haloalkylated aromatic ketone which serves as a free-radical intitiator for initiating polymerization of the acrylic compound, and a polymerizable organofunctional silane. Photographic elements, such as still films, motion picture films, paper prints, microfiche, and the like are provided with a protective overcoat layer which is permanently bonded to the element and serves to protect it from abrasion and scratches by coating the element with the radiation-curable composition and irradiating the coating to bond it to the element and cure it to form a transparent, flexible, scratch-resistant, crosslinked polymeric layer. The protective overcoat layer can be applied to the image bearing side of the element or to the support side of the element or to both sides. The radiation-curable composition can also be used as a restorative composition in the treatment of photographic elements which have scratches, abrasion marks, or the like which impair the appearance or projection capabilities of the element. In use as a restorative composition, the radiation-curable composition can be applied locally in the region of the defects only, to eliminate them effectively and restore the element to a substantially defect-free condition, or it can be applied over the entire surface of the element to both eliminate the defects and form a protective overcoat layer that is capable of providing protection against subsequent scratching or abrasion.
U.S. Pat. No. 4,092,173 (Novak et al.), the disclosure of which is totally incorporated herein by reference, discloses photographic elements, such as still films, motion picture films, paper prints, microfiche, or the like, which are provided with a protective overcoat layer which is permanently bonded to the element and serves to protect it from abrasion and scratches. The protective overcoat is formed by coating the element with a radiation-curable composition comprising an acrylated urethane, an aliphatic ethylenically-unsaturated carboxylic acid, and a multifunctional acrylate, and irradiating the coating to bond it to the element and cure it to form a transparent, flexible, scratch-resistant, crosslinked polymeric layer. Protective overcoat layers can be applied to the image-bearing side of the element or to the support side of the element or to both sides.
U.S. Pat. No. 4,954,364 (Stein et al.), the disclosure of which is totally incorporated herein by reference, discloses a method for enhancing the controlled release characteristics of paper or plastic substrates by applying onto the substrate a UV curable mixture of an epoxysilicone, an arylonium salt catalyst, such as diaryliodoniumhexafluoroantimonate, and a controlled release additive such as a phenolpropyl-substituted methyldisiloxane or an alkylphenol, such as dodecylphenol. The treated plastic or paper substrate is then subjected to UV irradiation to effect a tack-free cure of the UV curable mixture on the substrate.
U.S. Pat. No. 3,989,609 (Brack), the disclosure of which is totally incorporated herein by reference, discloses a prepolymer containing unsaturated hydrocarbon groups prepared and mixed on a roller mill with one or more acrylic ester monomers and various additives to make a coating formulation of a desired viscosity. In general, low viscosity formulations are used for overprint varnishes, on paper or foil, or with pigments, for certain types of printing inks. Higher viscosity formulations are used to apply thick films on panels, tiles or other bodies. Thin films are cured to hardness by brief exposure to ultraviolet light. Thicker films require more energetic radiation such as plasma arc and electron beam radiation. The prepolymers particularly useful for making such radiation curable coatings are the reaction products of polyether polyols and bis- or polyisocyanates and hydroxy alkenes or acrylic (or methacrylic) hydroxy esters, and, likewise, reactive polyamides modified with dicarboxy alkenes, their anhydrides, or esters. A small amount of wax incorporated in the coating formulations results in coatings with release characteristics similar to those of PTFE coatings.
Although known compositions and processes are suitable for their intended purposes, a need remains for processes for permanently affixing toned images to a variety of substrates, both porous and nonporous, and to substrates with a wide range of thermal conductivity, ductility, and thickness. In addition, a need remains for processes for permanently affixing toned images to substrates that enable improved color quality. It is believed that the process of the present invention, wherein the toner pile comprising the image is at least slightly dissolved in the overcoating material, spurious light scattering is decreased, thereby improving color quality. Further, there is a need for processes for permanently affixing toned images to substrates that minimize or eliminate the conventional high energy fusing step in the imaging process, such as the application of heat, pressure, or combinations thereof. The process of the present invention, wherein the overcoated toner pile comprising the image is cured to a solid, requires substantially less energy, thus reducing both the electrical power requirements and the ambient temperatures during development. Additionally, there is a need for processes for permanently affixing toned images to substrates that enable improved smoothness of the imaged substrate's surface. It is believed that the process of the present invention, wherein the toner image is overcoated with a curable material, improves surface smoothness, thereby improving image quality, particularly for color images and transparencies. Further, there is a need for processes for permanently affixing toned images to substrates that enable production of high quality transparencies with monochrome black or colored images thereon. Additionally, there is a need for processes for permanently affixing toned images to substrates that enable production of high quality transparencies with multi-colored images thereon. Further, typical electroscopic toners are fixed by heating on the substrate, which requires toner materials that melt easily (to lessen power requirements) but which don't conhere in machine ambient conditions. The process of the present invention enables the use of toners which can be at least partially soluble in the overcoating but which need not melt easily. The process of the present invention also enables the use of toners which melt at low temperatures, since the cured overcoating which is formed in the process prevents these toners from blocking or sticking to adjacent sheets in a stack.